Non-volatile memory bank and page buffer therefor

ABSTRACT

A memory system having a serial data interface and a serial data path core for receiving data from and for providing data to at least one memory bank as a serial bitstream. The memory bank is divided into two halves, where each half is divided into upper and lower sectors. Each sector provides data in parallel to a shared two-dimensional page buffer with an integrated self column decoding circuit. A serial to parallel data converter within the memory bank couples the parallel data from either half to the serial data path core. The shared two-dimensional page buffer with the integrated self column decoding circuit minimizes circuit and chip area overhead for each bank, and the serial data path core reduces chip area typically used for routing wide data buses. Therefore a multiple memory bank system is implemented without a significant corresponding chip area increase when compared to a single memory bank system having the same density.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.11/944,535, filed on Nov. 23, 2007, which claims the benefit of priorityof U.S. Provisional Patent Application No. 60/867,269, filed on Nov. 27,2006, the content of which is incorporated herein by reference in itsentirety.

BACKGROUND

Mobile electronic devices, such as, for example, digital cameras,portable digital assistants, portable audio/video players and mobileterminals continue to require mass storage memory, preferablynon-volatile memory with ever increasing capacities and speedcapabilities. For example, presently available audio players can havebetween 256 Mbytes to 40 Gigabytes of memory for storing audio/videodata. Non-volatile memory, for example, such as Flash memory andhard-disk drives are preferred since data is retained in the absence ofpower, thus extending battery life.

Presently, hard disk drives have high densities and can store 40 to 160Gigabytes of data, but are relatively bulky. However, Flash memory, alsoknown as a solid-state drive, is popular because of their high density,non-volatility, and small size relative to hard disk drives. The adventof multi-level cells (MLC) further increases the Flash memory densityfor a given area relative to single level cells. Those of skill in theart will understand that Flash memory can be configured as NOR Flash,NAND Flash or any other type of Flash memory configuration. NAND Flashhas higher density per given area due to its more compact memory arraystructure. For the purposes of further discussion, references to Flashmemory should be understood as being any type of Flash devices, such as,for example, NOR and NAND type Flash memory.

While existing Flash memory modules operate at speeds sufficient formany current consumer electronic devices, such memory modules likelywill not be adequate for use in future devices where high data rates aredesired. For example, a mobile multimedia device that records highdefinition moving pictures is likely to require a memory module with aprogramming throughput of at least 10 MB/s, which is not obtainable withcurrent Flash memory technology with typical programming data rates of 7MB/s. Multi-level cell Flash has a much slower rate of 1.5 MB/s due tothe multi-step programming sequence required to program the cells.

The problem with many standard memory devices lies in their use of aparallel data interface for receiving and providing data. For example,some memory devices provide 8, 16 or 32 bits of data in parallel at anoperating frequency of up to 30 MHz. Standard parallel data interfacesproviding multiple bits of data in parallel are known to suffer fromwell known communication degrading effects such as cross-talk, signalskew and signal attenuation, for example, which degrades signal quality,when operated beyond their rated operating frequency. In order toincrease data throughput, a memory device having a serial data interfacehas been disclosed in commonly owned U.S. Patent Publication No.20070076479, which receives and provides data serially at a frequency,for example, 200 MHz. The memory device described in U.S. PatentPublication No. 20070076479 can be used in a system of memory devicesthat are serially connected to each other, as described in commonlyowned U.S. Provisional Patent Application No. 60/902,003 filed Feb. 16,2007, the content of which is incorporated herein by reference in itsentirety.

FIG. 1A shows a system of a plurality of memory devices that areserially connected to each other, as described in U.S. PatentPublication No. 20070076479. Referring to FIG. 1A, a serialinterconnection 5 includes a plurality of memory devices that areconnected in series with a memory controller. The memory controllerincludes a system interface for receiving system commands and data fromthe system in which the serial interconnection is integrated, andprovides read data to the system. In particular, Device 0 is comprisedof a plurality of data input ports (SIP0, SIP1), a plurality of dataoutput ports (SOP0, SOP1), a plurality of control input ports (IPE0,IPE1), and a plurality of control output ports (OPE0, OPE1). These dataand control signals are sent to the memory device 5 from the memorycontroller. A second memory device (Device 1) is comprised of the sametypes of ports as Device 0. Device 1 is interconnected to Device 0. Forexample, Device 1 can receive data and control signals from Device 0.One or more additional devices may also be interconnected alongsideDevice 0 and Device 1 in a similar manner. A last device (e.g., Device3) in the series-connection provides data and control signals back tothe memory controller after a predetermined latency. Each memory device(e.g., device 0, 1, 2, 3) outputs an echo (IPEQ0, IPEQ1, OPEQ0, OPEQ1)of IPE0, IPE1, OPE0, and OPE1 (i.e., control output ports) to thesubsequent device. The signals can be passed from one device to asubsequent series-connected device. A single clock signal is provided toeach of the plurality of series-connected memory devices.

FIG. 1B is a block diagram illustrating the core architecture of one ofthe memory devices shown in FIG. 1A. Memory device 10 includes amultiplicity of identical memory banks with their respective data,control and addressing circuits, such as memory bank A 12 and memorybank B 14, an address and data path switch circuit 16 connected to bothmemory banks 12 and 14, and identical interface circuits 18 and 20,associated with each memory bank for providing data to and for receivingdata from the switch circuit 16. Memory banks 12 and 14 are preferablynon-volatile memory, such as Flash memory, for example. Logically, thesignals received and provided by memory bank 12 are designated with theletter “A”, while the signals received and provided by memory bank 14are designated with the letter “B”. Similarly, the signals received andprovided by interface circuit 18 are designated with the number “0”,while the signals received and provided by interface circuit 20 aredesignated with the number “1”. Each of the interface circuits 18 and 20receives access data in a serial data stream, where the access data caninclude a command, address information and input data for programmingoperations, for example. In a read operation, each of the interfacecircuits provides output data as a serial data stream in response to aread command and address data. The memory device 10 further includesglobal circuits, such as a control interface 22 and status/ID registercircuit 24, which provide global signals such as clock signal sclki andreset to the circuits of both memory banks 12 and 14 and the respectiveinterface circuits 18 and 20. A further discussion of the aforementionedcircuits now follows.

Memory bank 12 includes well known memory peripheral circuits such assense amplifier and page buffer circuit block 26 for providing outputdata DOUT_A and for receiving input program data DIN_A, and row decoderblock 28. Those of skill in the art will understand that block 26 alsoincludes column decoder circuits. A control and predecoder circuit block30 receives address signals and control signals via signal line ADDR_A,and provides predecoded address signals to the row decoders 28 and thesense amplifier and page buffer circuit block 26.

The peripheral circuits for memory bank 14 are identical to thosepreviously described for memory bank 12. The circuits of memory bank Binclude a sense amplifier and page buffer circuit block 32 for providingoutput data DOUT_B and for receiving input program data DIN_B, a rowdecoder block 34, and a control and predecoder circuit block 36. Controland predecoder circuit block 36 receives address signals and controlsignals via signal line ADDR_B, and provides predecoded address signalsto the row decoders 34 and the sense amplifier and page buffer circuitblock 36. Each memory bank and its corresponding peripheral circuits canbe configured with well known architectures.

In general operation, each memory bank is responsive to a specificcommand and address, and if necessary, input data. For example, memorybank 12 provides output data DOUT_A in response to a read command and aread address, and can program input data in response to a programcommand and a program address. Each memory bank can be responsive toother commands such as an erase command, for example.

In the example shown in FIG. 1B, path switch 16 is a dual port circuitwhich can operate in one of two modes for passing signals between thememory banks 12 and 14, and the interface circuits 18 and 20. First is adirect transfer mode where the signals of memory bank 12 and interfacecircuit 18 are passed to each other. Concurrently, the signals of memorybank 14 and interface circuit 20 are passed to each other in the directtransfer mode. Second is a cross-transfer mode where the signals ofmemory bank 12 and interface circuit 20 are passed to each other. At thesame time, the signals of memory bank 14 and interface circuit 18 arepassed to each other. A single port configuration of path switch 16 willbe discussed later.

As previously mentioned, interface circuits 18 and 20 receive andprovide data as serial data streams. This is for reducing the pin-outrequirements of the chip as well as to increase the overall signalthroughput at high operating frequencies. Since the circuits of memorybanks 12 and 14 are typically configured for parallel address and data,converting circuits are required.

Interface circuit 18 includes a serial data link 40, input serial toparallel register 42, and output parallel to serial register 44. Serialdata link 40 receives serial input data SIP0, an input enable signalIPE0 and an output enable signal OPE0, and provides serial output dataSOP0, input enable echo signal IPEQ0 and output enable echo signalOPEQ0. Signal SIP0 (and SIP1) is a serial data stream which can eachinclude address, command and input data. Serial data link 40 providesbuffered serial input data SER_IN0 corresponding to SIPO and receivesserial output data SER_OUT0 from output parallel to serial register 44.The input serial-to-parallel register 42 receives SER_IN0 and convertsit into a parallel set of signals PAR_IN0. The output parallel-to-serialregister 44 receives a parallel set of output data PAR_OUT0 and convertsit into the serial output data SER_OUT0, which is subsequently providedas data stream SOP0. Output parallel-to-serial register 44 can alsoreceive data from status/ID register 24 for outputting the data storedtherein instead of the PAR_OUT0 data. Further details of this particularfeature will be discussed later. Furthermore, serial data link 40 isconfigured to accommodate daisy chain cascading of the control signalsand data signals with another memory device 10.

Serial interface circuit 20 is identically configured to interfacecircuit 18, and includes a serial data link 46, input serial-to-parallelregister 48, and output parallel-to-serial register 50. Serial data link46 receives serial input data SIP1, an input enable signal IPE1 and anoutput enable signal OPE1, and provides serial output data SOP1, inputenable echo signal IPEQ1 and output enable echo signal OPEQ1. Serialdata link 46 provides buffered serial input data SER_IN1 correspondingto SIP1 and receives serial output data SER_OUT1 from outputparallel-to-serial register 50. The input serial-to-parallel register 50receives SER_IN1 and converts it into a parallel set of signals PAR_IN1.The output parallel-to-serial register 48 receives a parallel set ofoutput data PAR_OUT1 and converts it into the serial output dataSER_OUT1, which is subsequently provided as data stream SOP1. Outputparallel to serial register 48 can also receive data from status/IDregister 24 for outputting the data stored therein instead of thePAR_OUT1 data. As with serial data link 40, serial data link 46 isconfigured to accommodate daisy chain cascading of the control signalsand data signals with another memory device 10.

Control interface 22 includes standard input buffer circuits, andgenerates internal chip select signal chip_sel, internal clock signalsclki, and internal reset signal reset, corresponding to chip select(CS#), serial clock (SCLK) and reset (RST#), respectively. While signalchip_sel is used primarily by serial data links 40 and 46, reset andsclki are used by many of the circuits throughout memory device 10.

While the serial data interface provides performance advantages overparallel data interface architectures, these advantages can be offset byperformance degradations in memory banks 12 and 14. More specifically,the push for increased memory density will adversely affect how quicklydata can be sensed from the memory cells, especially NAND configuredFlash memory cells. To illustrate this problem, a portion of a NANDconfigured Flash memory array of FIG. 1B is shown in FIG. 2.

Referring to FIGS. 1B and 2, memory bank 12 includes i sets of bitlines,where i is an integer number greater than 0, and each set includes aneven bitline and an odd bitline. For example, bitline set 1 includeseven bitline BL1 _(—) e and odd bitline BL1 _(—) o. Each bitline isconnected to at least one NAND cell string, where each NAND cell stringincludes a plurality of non-volatile memory cells and access transistorsconnected in series between the respective bitline and a common sourceline CSL. The access transistors include a source select transistor forreceiving a source select line signal SSL, and a ground selecttransistor for receiving a ground select line signal GSL. Connectedserially between these two access transistors are a plurality ofnon-volatile memory cells, such as Flash memory cells. In the presentexample, there are 32 serially connected Flash memory cells, having gateterminals coupled to respective wordlines WL1 to WL32.

Sense amplifier and page buffer circuit block 26 includes i page bufferunits 60, or one for each bitline set. Because the bitline pitch isnarrow, a page buffer unit 60 is shared between the even and oddbitlines of a bitline set. Therefore selection transistors receivingeven and odd selection signals BSLe and BLSo are required for selectingone bitline of the set to be coupled to the page buffer unit 60. Eachpage buffer unit 60 senses and latches data from the bitlines, and thoseskilled in the art will understand that the page buffer latches writedata to be programmed. Each NAND cell string sharing common wordlinesWL1-WL32, SSL, and GSL lines is referred to as a memory block, while thememory cells connected to one common wordline is referred to as a page.Those skilled in the art should understand how Flash read, program anderase operations are executed.

FIG. 3 is a circuit schematic of column select circuits of the senseamplifier and page buffer circuit block 26 for coupling data in the pagebuffer units 60 of FIG. 2 to data lines. The present example of FIG. 3illustrates one possible logical decoding scheme, where a preset numberof page buffers are associated with each of 16 data lines DL1 to DL16.In the present example, there are 16 identically configured datalinedecoder circuits 70, one being coupled to each of datelines DL1 to DL16.The following description refers to the dataline decoder circuit 70coupled to DL1. Dateline decoder circuit 70 includes 16 groupings of 32page buffer units 60. In each grouping, the input/output terminal of onepage buffer unit is coupled to a respective first stage n-channel passtransistor 72. All the first stage n-channel pass transistors areconnected in parallel and controlled by first stage selection signalsYA1 to YA32 to selectively couple one page buffer unit 60 to one secondstage n-channel pass transistor 74. Since there is one second stagen-channel pass transistor 74 per grouping, there are a total of 16second stage n-channel pass transistors 74 connected in parallel to DL1,each controlled by respective second stage selection signals YB1 toYB16. Because signals YA1 to YA32 and YB1 to YB16 are shared across allthe dataline decoder circuits 70, the activation of one first stageselection signal and one second stage selection couples one page bufferunit 60 from each dataline decoder circuit 70, to a correspondingdataline.

In a read, program verify and erase verify operation, the cell data inthe selected page should be sensed and latched in their correspondingpage buffer units 60. Column decoding then selects which page bufferunits to couple to the datalines. Sensing is dependent on the cellcurrent generated by a selected memory cell, and the cell current isdependent on the number of cells in the NAND cell string. In the exampleof FIG. 2, the cell current is typically less than 1 (μA) for a 32 cellNAND string manufactured with a 90 nm process technology. Unfortunately,the push to increase memory array density to lower device cost resultsin the addition of more memory cells per NAND cell string. As a result,this cell current will further decrease, thereby requiring moresensitive sensing circuits and/or sensing time. Further compounding thisproblem is the bitline RC delay due to the physical length of thebitline, and junction capacitance of the NAND cell string as the numberof cells per NAND cell string is increased. These physical changes incombination with advanced manufacturing process for reducing featuresizes further exacerbates the cell current problem. This problem withcell current is well known, as demonstrated by June Lee et al., “A 90-nmCMOS 1.8-V 2-Gb NAND Flash Memory for Mass Storage” Applications,” IEEEJ. Solid-State Circuits, vol. 38, pp. 1934-1942, November 2003. Anotherfurther problem related to using advanced manufacturing processes isyield, where long bitlines introduce process uniformity issue acrossprocess steps, thereby reducing the yield per wafer as the potential fordefects increases.

One possible solution to this problem may be to limit the number ofmemory cells per NAND cell string, and divide large memory arrays intomultiple memory banks. An advantage of having multiple memory banks isthe capability of transferring data directly between the memory bankswithout having to transfer data out from the memory device. Thedisadvantage of using multiple memory banks is that each bank requiresits own set of sense amplifier and page buffer circuit block 26, therebyincreasing additional circuit overhead and chip area. The complexcircuitry and area overhead required for implementing direct bank tobank data transfer also consumes additional chip area.

SUMMARY

In a first aspect, the present invention provides a memory system. Thememory system includes a memory bank and a serial data path. The memorybank provides serial bitstream read data in response to a read operationand receives serial bitstream write data in response to a writeoperation. The serial data path couples the serial bitstream read dataand the serial bitstream write data between the memory bank and aninput/output interface. According to one embodiment, the serial datapath includes a data arbitrator for receiving access data serially fromthe input/output interface, the access data including a command and anaddress. The data arbitrator converts the command and the address into aparallel format and passes the serial bitstream read data to theinput/output interface during the read operation. According to anotherembodiment, the memory bank includes a first bank half, a second bankhalf and a parallel/serial data converter. The first bank half iscoupled to first n parallel datalines, where n is an integer valuegreater than 0. The second bank half is coupled to second n paralleldatalines. The parallel/serial data converter selectively converts oneof the first and the second n parallel datalines into the serialbitstream read data and selectively converts the serial bitstream writedata into parallel data for one of the first and the second n paralleldatalines.

In an aspect of the present embodiment, the first bank half includes afirst sector, a second sector and a first page buffer. The first sectorhas wordlines and bitlines coupled to memory cells. The second sectorhas wordlines and bitlines coupled to memory cells. The first pagebuffer is selectively coupled to bitlines of one of the first sector andthe second sector, and is coupled to the first n parallel datalines. Thesecond bank half includes a third sector, a fourth sector and a secondpage buffer. The third sector has wordlines and bitlines coupled tomemory cells. The fourth sector has wordlines and bitlines coupled tomemory cells. The second page buffer is selectively coupled to bitlinesof one of the third sector and the fourth sector, and is coupled to thesecond n parallel datalines. In the present aspect, the bitlines of thefirst sector and the second sector are grouped into sets of bitlines,where each of the sets of bitlines are coupled to a common bitline, andthe common bitline is coupled to the first page buffer. Similarly, thebitlines of the third sector and the fourth sector are grouped into setsof bitlines, where each of the sets of bitlines is coupled to a commonbitline, and the common bitline is coupled to the second page buffer.

In another aspect of the present embodiment, the parallel/serial dataconverter includes a first parallel/serial data converter, a secondparallel/serial data converter and a data path selector. The firstparallel/serial data converter sequentially couples each of the first nparallel datalines to a first terminal. The second parallel/serial dataconverter sequentially couples each of the second n parallel datalinesto a second terminal. The data path selector selectively couples one ofthe first terminal and the second terminal to a bidirectional serialdata line. The memory system can further include control logic forreceiving a command and an address for operating the memory bank, theparallel/serial converter and the serial data path during the readoperation.

In yet another embodiment of the present aspect, the memory systemfurther includes another memory bank for providing the serial bitstreamread data in response to the read operation and for receiving the serialbitstream write data in response to the write operation. In the presentembodiment, the serial data path includes a data switcher forselectively coupling the serial bitstream write data to one of thememory bank and the other memory bank. Furthermore, the serial data pathselectively couples the serial bitstream read data from one of thememory bank and the other memory bank to the data arbitrator of theserial data path. In an alternate embodiment, the memory system furtherincludes another serial data path for coupling the serial bitstream readdata from one of the memory bank and the other memory bank to anotherinput/output interface. The other serial data path also couples theserial bitstream write data to one of the memory bank and the othermemory bank. The other serial data path can include a second dataswitcher for selectively coupling the serial bitstream write data to oneof the other memory bank and the data switcher, and for selectivelycoupling the serial bitstream read data to one of the data switcher andanother data arbitrator. A serial transfer dataline is provided forcoupling the data switcher to the second data switcher. The memorysystem can further include a serial transfer switch for selectivelycoupling the serial bitstream read data from one of the memory bank andthe other memory bank to the serial data path.

The present invention may provide a method for use in a memory system.The method includes: providing serial bitstream read data in response toa read operation and receiving serial bitstream write data in responseto a write operation; and coupling the serial bitstream read data andthe serial bitstream write data between the memory bank and aninput/output interface.

In a second aspect, the present invention provides a memory bank. Thememory bank includes a memory array, a page buffer and a sequentialcoupler. The memory array has memory cells connected to bitlines andwordlines. The page buffer latches data of the bitlines during a readoperation, and couples the latched data to a predetermined number ofdatelines in parallel. The sequential coupler sequentially couples eachof the predetermined number of datelines to a bidirectional serial dataline. The sequential coupler can include a parallel/serial dataconverter having terminals coupled to each of the predetermined numberof datelines. The parallel/serial data converter is controllable tosequentially couple each of the terminals to the bidirectional serialdata line. The memory bank can further include a counter responsive to aclock signal for controlling the first parallel/serial data converterand the second parallel/serial data converter. The data path selector iscontrolled by a most significant bit of the counter not used by firstparallel/serial data converter and the second parallel/serial dataconverter.

In an alternate embodiment, the sequential coupler can include a firstparallel/serial data converter, a second parallel/serial data converterand a data path selector. The first parallel/serial data converter hasfirst terminals coupled to each of the predetermined number ofdatelines, and the first parallel/serial data converter is controllablefor sequentially coupling each of the first terminals to a first localbidirectional serial data line. The second parallel/serial dataconverter has second terminals coupled to each of the predeterminednumber of second datelines, and the second parallel/serial dataconverter is controllable for sequentially coupling each of the secondterminals to a second local bidirectional serial data line. The datapath selector selectively couples one of the first local bidirectionalserial data line and the second local bidirectional serial data line toa global bidirectional serial data line.

The present invention may provide a method for use a memory array havingmemory cells connected to bitlines and wordlines. The method includes:latching data of the bitlines during a read operation, and for couplingthe latched data to a predetermined number of datalines in parallel; andsequentially coupling each of the predetermined number of datalines to abidirectional serial data line.

In a third aspect, the present invention provides a memory bank. Thememory bank includes a first memory sector, a second memory sector and apage buffer. The first memory sector has memory cells connected to firstbitlines and first wordlines, where the first bitlines are arranged as msegments where m is an integer value greater than 0. The second memorysector has memory cells connected to second bitlines and secondwordlines, where the second bitlines being arranged as m segments. Thepage buffer selectively couples one of the first bitlines and the secondbitlines of each of the m segments to a predetermined number ofdatalines. In an embodiment of the present aspect, a read operation isexecuted by activating a wordline of one of the first wordlines in thefirst memory sector and the second wordlines in the second memory sectorin response to a row address, where at least two memory cells arecoupled to the first bitlines when the wordline is one of the firstwordlines, and at least two memory cells are coupled to the secondbitlines when the wordline is one of the second wordlines; selectivelycoupling one bitline of the first bitlines and the second bitlines to acommon bitline in response to a column address; sensing the commonbitline with the page buffer; and providing data corresponding to thesensed common bitline onto one of the predetermined number of datalines.

The present invention may provides a method for use in a memory bankhaving memory cells connected to first bitlines and first wordlines, thefirst bitlines being arranged as m segments where m is an integer valuegreater than 0. The method includes: selectively coupling one of thefirst bitlines and the second bitlines of each of the m segments to apredetermined number of datalines.

In a fourth aspect, the present invention provides a page buffer for amemory bank. The page buffer including a first self-decoding page bufferstage and a second self-decoding page buffer stage. The firstself-decoding page buffer stage senses data from a first set of commonbitlines, and provides sensed data. The sensed data corresponds to eachof the common bitlines of the first set of common bitlines, which areprovided on corresponding data lines in response to an active columnselect bit latched in a clock signal state. The second self-decodingpage buffer stage senses data from a second set of common bitlines, andprovides sensed data. The sense data corresponds to each of the commonbitlines of the second set of common bitlines, which are provided on thecorresponding data lines in response to the active column select bitlatched in a subsequent clock signal state. In an embodiment of thepresent aspect, a self-decoding operation is executed by latching theactive column select bit in the first self-decoding page buffer stage inresponse to an opposite clock signal state; providing the sensed datafrom the first self-decoding page buffer stage and passing the activecolumn select bit in response to the clock signal state; latching theactive column select bit in the second self-decoding page buffer stagein response to a subsequent opposite clock signal state; and providingthe sensed data from the second self-decoding page buffer stage inresponse to the subsequent clock signal state.

The present invention may provide a method for use in a page buffer fora memory bank. The method includes: sensing data from a first set ofcommon bitlines, and for providing sensed data corresponding to each ofthe common bitlines of the first set of common bitlines on correspondingdata lines in response to an active column select bit latched in a clocksignal state; and sensing data from a second set of common bitlines, andfor providing sensed data corresponding to each of the common bitlinesof the second set of common bitlines on the corresponding data lines inresponse to the active column select bit latched in a subsequent clocksignal state.

In a fifth aspect, the present invention provides a system. The systemincludes a memory controller for providing access data and a serialinterconnection of a plurality of memory devices. Each of the memorydevices includes a controller, a memory bank and a serial data path. Thecontroller receives the access command and an address contained inaccess data, for executing an operation corresponding to the accesscommand. The memory bank executes the operation in accordance with theaccess command to access data stored in a memory location addressed bythe address. The serial data path couples the data in serial formatbetween the memory bank and an input/output interface.

For example, the plurality of memory devices are connected in series andthe memory controller sends the access command of an instruction, suchas for example, read and write commands. In a read operation, the memorydevice performs a data read operation and forwards the read data to anext memory device or the memory controller. In a write operation, thememory device performs a data write operation based on data provided bythe memory controller or a previous memory device. The system, thememory controller and the devices may perform such methods as operatingthe controller and devices.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1A shows a system of a plurality of memory devices seriallyconnected to each other;

FIG. 1B is a block diagram of a memory device having a serial datainterface;

FIG. 2 is a circuit schematic showing NAND cell strings coupled to asense amplifier and page buffer circuit block of FIG. 1B;

FIG. 3 is a circuit schematic showing a column decoding scheme used withthe amplifier and page buffer circuit block shown in FIG. 2;

FIG. 4A is a block diagram of a non-volatile memory serial core systemaccording to an embodiment of the present invention;

FIG. 4B is a block diagram of illustration of details of a serial datapath shown in FIG. 4A;

FIG. 5 is a block diagram of a memory bank of FIG. 4A, according to anembodiment of the present invention;

FIG. 6 is a circuit schematic embodiment of the parallel/serial dataconverter shown in FIG. 5;

FIG. 7A is a block diagram showing details of two sectors of the memorybank of FIG. 5;

FIG. 7B is a circuit schematic embodiment showing the bitlinearrangement of the sectors shown in FIG. 5;

FIG. 8 is a circuit schematic embodiment of a decoding circuit forcontrolling the bitline selection circuit of FIG. 7;

FIG. 9 is a circuit schematic of the charge pump shown in FIG. 8;

FIG. 10 is a block diagram showing a self-decoding column selectcircuit, according to an embodiment of the present invention;

FIG. 11 is a block diagram showing the details of one self-decoding pagebuffer cell, according to an embodiment of the present invention;

FIG. 12 is a circuit schematic of a sequential enabler in theself-decoding page buffer cell of FIG. 11, according to an embodiment ofthe present invention;

FIG. 13 is a circuit schematic of a page buffer unit in theself-decoding page buffer cell of FIG. 11, according to an embodiment ofthe present invention;

FIG. 14 is a sequence diagram illustrating the operation of theself-decoding column select circuit of FIG. 10;

FIG. 15 is a block diagram illustrating a two bank configuration havinga serial core architecture, according to an embodiment of the presentinvention;

FIG. 16 is a circuit schematic of the serial transfer switch shown inFIG. 15, according to an embodiment of the present invention; and,

FIG. 17 is a block diagram of a multi-bank serial core memory systemhaving two independent serial data paths, according to an embodiment ofthe present invention;

DETAILED DESCRIPTION

Generally, the present invention provides a memory system having aserial data interface and a serial data path core for receiving datafrom and for providing data to at least one memory bank as a serialbitstream. The memory bank is divided into two halves, where each halfis divided into upper and lower sectors. Each sector provides data inparallel to a shared two-dimensional page buffer with an integrated selfcolumn decoding circuit. A serial to parallel data converter within thememory bank couples the parallel data from either half to the serialdata path core. The shared two-dimensional page buffer with theintegrated self column decoding circuit minimizes circuit and chip areaoverhead for each bank, and the serial data path core reduces chip areatypically used for routing wide data buses. Therefore a multiple memorybank system is implemented without a significant corresponding chip areaincrease when compared to a single memory bank system having the samedensity.

FIG. 4A is a block diagram of a non-volatile memory serial core systemaccording to an embodiment of the present invention. Serial core memorysystem 100 includes a serial data path 102 for coupling a serialbitstream of data between external input/output interface pins calledthe DATA/CMD_IN and DATA/CMD_OUT pins and at least one memory bank 104.A memory bank is understood to include pitch-limited circuits, such asrow decoders, sense amplifiers, page buffers, column decoding circuitry,and any other circuits which are formed proximate to the rows andcolumns of memory cells that make up the memory array. Such circuits areformed proximate to the memory array to maximize the packing density ofthe circuits while minimizing the transmission path of electricalsignals, such as bitline currents and wordline voltages. Otherfunctional blocks of serial core memory system 100 includes a controlblock 106 and a high voltage generator 108 for providing the necessaryvoltage levels needed to program and erase the non-volatile memory cellsof memory bank 104. The control block 106 includes a command decoder,registers, and other related control circuits (not shown) that are usedto govern operation of the serial core memory system 100.

According to the present embodiment, the memory bank 104 is configuredto provide read data and to receive write data (for programming), in aserial bitstream. In the example shown in FIG. 4A, both the read dataand the write data share a bidirectional serial data line 110, howeveralternate embodiments can have dedicated input and output unidirectionaldata lines. In the embodiment of FIG. 4A, the serial data path 102receives the serial read data and passes it to the DATA/CMD_OUT pin inthe serial format, and passes serial write data to the memory bank 104received from the DATA/CMD_IN pin. Therefore, in both read and writeoperations, the data is maintained in the serial format between thememory bank and the data I/O pins. Further details of the serial datapath 102 will now be described.

The serial data path 102 is primarily responsible for coupling read orwrite data in a serial format between the memory bank 104 and either ofthe DATA/CMD_IN pin and the DATA/CMD_OUT pin. Optionally, the serialdata path 102 can selectively couple read or write data between two ormore memory banks and either the DATA/CMD_IN pin and the DATA/CMD_OUTpin. In another alternate embodiment, the serial data path 102 cancouple read data directly between two different memory banks. The serialdata path 102 includes a serial I/O interface 112, a data arbitrator114, and a data switcher 116.

FIG. 4B shows details of the serial data path 102 shown in FIG. 4A.Referring to FIGS. 4A and 4B, the serial I/O interface 112 is connecteddirectly to the DATA/CMD_IN and the DATA/CMD_OUT pins. The serial I/Ointerface 112 can be similarly configured to the serial data link 40 ofFIG. 1B and include the same circuitry described for it in U.S. PatentPublication No. 20070076479. In the present example, additional controlinput signals shown in serial data link 40 of FIG. 1B are not shown inorder to simplify the schematic. Generally, the serial I/O interface 112receives and buffers the externally received input data signals, and caninclude pass through circuits for directly coupling data from theDATA/CMD _IN pin to the DATA/CMD_OUT pin. This feature is used to passany command with optional data to another memory device if the commandis not intended for the current memory device. The serial I/O interface112 includes input buffers 120 for receiving serial input data from itsDATA/CMD_IN pin, and output buffers or output driver 122 for providingread data and pass through data through its DATA/CMD_OUT pin. The inputbuffers 120 and output drivers 122 are controlled by one or more buffercontrol signals received from the control block 106, referred to asB_CTRL in FIG. 4A.

The data arbitrator 114 receives the serial data from the serial I/Ointerface 112. The data arbitrator 114 includes a command data converter124 and a path switch 126. The command data converter 124 converts onlythe command data from the serial format into a parallel format, which isthen sent to the control block 106 as parallel command signal COMMAND.The path switch 126 selectively connects the serial I/O interface 112 toeither the command data converter 124 of the data switcher 116 inresponse to a switch signal from the control block 106 (not shown).Command data converter 124 can include a serial/parallel shift registerthat serially receives the command data on each active clock edge, andhas parallel outputs from each stage of the shift register for providingthe parallel command. Serial/parallel shift registers are known in theart. Since the data structure of the access data is predetermined, forexample the command data can be the first two bytes followed by writedata, the control block 106 will know when all the command data bitshave been loaded into the command data converter 124 by counting thenumber of clock edges that have passed. Any write data that is receivedremains in the serial format, and is passed serially to the dataswitcher 116. Accordingly, command data converter 124 will only receivethe command data while the data switcher will only receive the writedata.

The data switcher 116 includes another path switch 128 which iscontrolled by signal SWTCH from the control block 106, to couple serialdata between the memory bank and the data arbitrator 114, or to coupleserial data between two different memory banks via corresponding serialtransfer dateline 118. If there are no other memory banks on the chip,then data switcher 116 is not required and the serial data is provideddirectly to memory bank 104 from data arbitrator 114.

The operation of the serial core memory system 100 in a read and awrite/program operation is now described. In a read operation, it ispresumed that a serial read command is received at the DATA/CMD_IN pin,which is then converted into the parallel format and sent to thecontroller 106 by data arbitrator 114. The controller 106 then activatesthe appropriate rows and columns in the memory bank 104 to access thedesired data. The memory bank 104 is then controlled to provide the readdata in a serial bitstream to the data switcher 116. If the read data isto be output to the DATA/CMD_OUT pin, then the data switcher 116 will becontrolled to pass the read data to the data arbitrator 114, whichsimply passes the read data to the serial I/O interface 112 for outputvia the DATA/CMD_OUT pin.

In a write or program operation, serial data received on the DATA/CMD_INpin includes a command and write data. The command data includes addressdata to which the write data is to be programmed. The command data isconverted to the parallel format by data arbitrator 114 and passed tocontrol block 106. It is noted that the command is received before thewrite data in the serial bitstream, so that decoding of the command canbe executed for initiating circuits for the programming operation as thewrite data is passed to the memory bank 104. Because the control block106 has received a program command, the appropriate programmingalgorithms are executed and the proper program voltages are applied, toensure that the write data is programmed to the target address.Additional algorithms such as program verify will also be executed torepeat the programming, if necessary.

As previously described in FIG. 4A, the memory bank 104 provides andreceives serial data. However, as persons skilled in the art willunderstand, memory arrays such as Flash memory are inherently parallelin nature. This means that more than one bit of data is accessed fromthe memory array and written to the memory array in any single read orwrite operation, respectively. According to the present embodiment ofmemory bank 104, an internal parallel/serial converter is provided forconverting serial data into a parallel format, and vice versa. Morespecifically, read data provided in parallel from bitlines of the memoryarray is converted into serial format, and serial write data isconverted into parallel format for simultaneous application to bitlinesof the memory array. Furthermore, the memory bank 104 is configured tomaximize wordline and bitline performance by segmenting the memory arrayinto sections along both the wordline and the bitline directions.

FIG. 5 is a block diagram illustrating an example embodiment of thememory bank 104 of FIG. 4A, according to an embodiment of the presentinvention. Memory bank 200 is divided into four memory portions, shownas sectors (sector 1, sector 2, sector 3 and sector 4) 202, 204, 206 and208. In the physical orientation of the memory bank 200 of FIG. 5, eachsector includes bitlines extending in the vertical direction andwordlines extending in the horizontal direction. By example, the memorycells can be organized as Flash NAND cell strings similar to those shownin FIG. 2. For driving the wordlines, each sector includes a wordlinedriver block 210, which can include associated decoding logic foractivating a selected wordline during read and program operations. Inthe present embodiment, the wordline driver blocks 210 corresponding tosectors 202 and 204 activate the same logical wordline of a row inresponse to a row address within a first address range, while thewordline driver blocks 210 corresponding to sectors 206 and 208 activatethe same logical wordline of a row in response to a row address within asecond address range. In other words, the rows of memory bank 200 areaccessed in the same manner as a traditional memory array consisting ofa single large sector having the same number of rows. However, wordlineperformance is improved since each wordline row is divided into shortersegments that are driven by their own wordline driver blocks 210.Accordingly, the central location of the wordline driver blocks 210divide the memory bank into left and right bank halves, where sectors202 and 206 form the left half and sectors 204 and 208 form the righthalf.

For sensing bitline data and latching program data, sectors 202 and 206have their bitlines coupled to shared page buffer 212, while sectors 204and 208 have their bitlines coupled to shared page buffer 214.Accordingly, sectors 202 and 204 can be referred to as lower sectorswhile sectors 206 and 208 can be referred to as upper sectors. Pagebuffers 212 and 214 are configured to be selectively coupled to one ofan upper sector and a lower sector, thereby overcoming the need to haveseparate sets of page buffers for each sector. This contributes to thearea minimization of the area of memory bank 200. Further details of theshared page buffers 212 and 214 will be described later. Page buffers212 and 214 sense and latch in parallel, bitline data in response to anactivated wordline during a read operation. The data associated with thememory cells connected to a single wordline is commonly referred to as apage of data. In the presently described configuration of FIG. 5 wherewordlines in both halves of the memory bank are logically the same, pagebuffer 212 senses and latches a first half page of data and page buffer214 senses and latches a second half page of data. As those skilled inthe art would understand, the page buffers 212 and 214 sense and latchthe bitline data in parallel upon activation of the selected wordline.Once latched, this read data will eventually be output as a serialbitstream.

As will be shown later, a first set of input/output datelines is coupledto page buffer 212, and a second set of input/output datelines iscoupled to page buffer 214. The width of the sets of datelines will be nbits wide, where n is an integer value greater than 1. Located betweenthe two halves is a parallel/serial data conversion selector (P/SCS)216, which functions as a sequential coupler, that is coupled to thesets of datelines coupled to page buffers 212 and 214. Theparallel/serial data conversion selector 216 is placed such that bothsets of datelines are the same physical length, and preferably a minimumphysical length to minimize loading capacitance. In the presentembodiment, the parallel/serial conversion selector 216 convertsparallel data from the shared buffer 212 to serial format onto dateline110 or converts parallel data from the shared buffer 214 to serialformat onto bidirectional serial dateline 110. More specifically, eachof the n datelines is sequentially coupled to the single bidirectionalserial data line 110 as a signal called GLOB_DATA. The parallel/serialconversion selector 216 converts serial data on bidirectional serialdata line 110 to parallel format for the n datelines coupled to sharedpage buffer 212 or shared page buffer 214. For example, theparallel/serial conversion selector 216 is controlled to couple each ofthe n datelines corresponding to page buffer 212 to bidirectional serialdata line 110, followed by each of the n datelines corresponding to pagebuffer 214.

Following is an example for illustrating the relationship of the numberof datelines and the half page size of data stored in either of pagebuffers 212 and 214. For example, if page buffer 212 latches a 1024 bithalf page, and the dateline is 16 bits wide, then parallel/serialconversion selector 216 will cycle through 1024/16=64 sets of 16 bitwide data. Once all 1024 bits are serially output onto serial data line110, then the next 1024 bits from page buffer 214 are provided. Detailsof this implementation will be shown later. A program operation is thereverse process of the read operation in which serial write data isprovided on serial data line 110. In the present example, 16 bits areapplied in parallel to the page buffer 212 via the 16 datelines in eachcycle.

The embodiment of FIG. 5 shows a memory bank 200 having left and righthalves. In an alternate configuration, the memory array includes onlytwo sectors, such as sectors 202 and 206. Sector 206 can thus be theaggregate size of sectors 206 and 208 and sector 202 can be theaggregate size of sectors 202 and 204. In such configuration, a fullpage of data would be latched by page buffer 212.

FIG. 6 is a circuit schematic of parallel/serial data converter 216according to an embodiment of the present invention. Referring to FIG.6, the P/S data conversion selector 216 includes a first parallel/serialdata converter (P/SDC) 300, a second P/SDC 302, and a data path selector304. P/SDC 300 and P/SDC 302 can be implemented as identicalbidirectional n to 1 multiplexor/demultiplexor switches, and data pathselector 304 can be implemented as is a bidirectional 2 to 1multiplexor/demultiplexor switch. P/SDC 300 selectively couples each ofthe left side datalines L_DL1 to L_DLn to the local bidirectional serialdata line L_DATA terminal, while P/SDC 302 selectively couples each ofthe right side datalines R_DL1 to R_DLn to the local bidirectionalserial data line R_DATA terminal. Data path selector 304 selectivelycouples either L_DATA or R_DATA to the global bidirectional serial dataline 110 as GLOB_DATA. In order to sequentially couple each of thedatalines to the output, a counter 306 can be used to provide outputsthat are decoded within P/SDC 300 and P/SDC 302 in response to a clockedsignal CLK. Such counter decoding schemes should be well known to thoseof skill in the art. Accordingly, L_DATA and R_DATA are n bits in lengthfor one cycle of the counter. Data path selector 304 is controlled by aselection control signal HALF_SEL to allow all n bits of L_DATA to passthrough in one logic state, and to allow all n bits of R_DATA to passthrough in the opposite logic state. Signal HALF_SEL can be generated bythe control block 106 of FIG. 4A in relation to a column address thatcan select which half of the memory bank 200 is to be accessed. In theembodiment of FIG. 6, counter 306 is shared with P/SDC 300 and P/SDC 302to minimize circuit overhead since dedicated counters wouldunnecessarily consume chip area.

A seamless transition between the L_DATA and R_DATA bits is achieved bycoupling signal HALF_SEL to a most significant bit (MSB) that is notused by P/SDC 300 or P/SDC 302, and will toggle states after the lastdataline (L_DLn or R_DLn) is coupled to the L_DATA or R_DATA terminal.Using P/SDC 300 for example, if n=4, there will be a total of fourdatalines (L_DL1 to L_DL3), and a two bit signal is required toselectively couple each of the four data lines to L_DATA. Because theoutputs of counter 306 are coupled to P/SDC 300 and P/SDC 302, they willswitch at the same time. However, the state of HALF_SEL will dictatewhether L_DATA or R_DATA is passed onto GLOB_DATA. Therefore, a thirdand most significant bit can be used to control HALF_SEL, which willchange states only after the fourth and last dataline L_DL4 is coupledto L_DATA. Table 1 below steps through a sequence using the n=4 example.

TABLE 1 Bit 2 State HALF_SEL Bit 1 Bit 0 1 0 0 0 2 0 0 1 3 0 1 0 4 0 1 15 1 0 0 6 1 0 1 7 1 1 0 8 1 1 1

In states 1 to 4, Bit 2 remains at the low logic state, while Bit 1 andBit 2 are used by P/SDC 300 to couple L_DL1 to L_DL4 to L_DATA. Startingat state 5, Bit 2 toggles to the high logic state as the counterincrements, and remains at the high logic state until state 8. Bit 1 andBit 2 “restart” at state 5 and gradually increment as in states 1 to 4.Accordingly, Bit 2 is suitable as the HALF_SEL control signal as itinherently controls when data path selector 304 is to switch over fromL_DATA to R_DATA.

Now that the parallel/serial data conversion selector (P/SCS) 216 hasbeen discussed, details of the memory bank sectors and page buffers ofFIG. 5 will be described with reference to FIGS. 7A to 11. FIG. 7A is anenlarged schematic of sectors 202 and 206 with shared page buffer 212.More specifically, FIG. 7A illustrates subdivisions of sectors 202 and206, referred to as segments. In the present example, sector 202 isdivided into four equally sized and identically configured segments 402while sector 206 is divided into four equally sized and identicallyconfigured segments 400. The selection of four segments per sector is byexample only, as those skilled in the art will understand that thenumber of segments per sector is a design parameter for the memory bank.As will be shown in further detail in FIG. 7B, each segment 400 and 402includes the same number of bitlines. FIG. 7B is a schematic showing onesector 400, one segment 402, and their interconnection with page buffer212 of shown in FIG. 7A. Segments 400 and 402 can each provide n bits ofdata via data lines L_DL[1:n] in any single read operation.

The bitlines of each segment 400 and 402 are arranged as sets ofbitlines, and in the present example of FIG. 7B, each set includes evenand odd bitlines BL1 _(—) e/BL1 _(—) o to BLn_(—) e/BLn_(—) o. Each setof even and odd bitlines is selectively coupled to respective commonbitlines CBL_S1_1 to CBL_S1 _(—) n, and each common bitline is coupledto page buffer 212. The term “S1” indicates that the common bitline CBLbelongs to the first segment (400 or 402) of the sector, and the lastdigit indicates the specific common bitline of the first segment. Thebitlines of segment 400 are identically configured to those of segment402. In the present embodiment, bitline BL1 _(—) e of segment 402 islogically the same as bitline BL1 _(—) e of segment 400, as are theother bitlines having common labels. In other words, the bitlines ofsegments 402 and 400 in the present configuration are equivalent to asingle bitline of memory bank 12 of FIG. 2. The advantage of dividingbitlines into two physical sections is that the bitlines of each sectorare half as long as the bitlines of memory bank 12. By reducing thelength of the bitline as seen by each NAND cell string connected to it,the capacitive loading of the bitline is significantly reduced. Hence,each NAND cell string can be configured to have more cells, therebyincreasing the density of the memory array.

In addition to the Flash memory cells, the source select transistor andthe ground select transistor, each set of even and odd bitlines ofsegments 400 and 402 further include a program disable circuit and aneven/odd bitline selection circuit coupled thereto. The description ofthese two circuits coupled to BL1 _(—) e and BL1 _(—) o of segment 400follows. The bitline selection circuit 405 includes high voltagen-channel transistors 404 and 406, where transistor 404 selectivelycouples BL1 _(—) e to a common bitline CBL_S1_1 and transistor 406selectively couples BL1 _(—) o to common bitline CBL_S1_1. Commonbitline CBL_S1_1 is connected to page buffer 212, and to the bitlineselection circuit of segment 402. N-channel transistors 404 and 406 arecontrolled by decoded even and odd selection signals A_SELe and A_SELorespectively. The prefix “A” denotes signals associated with segment400, while prefix “B” denotes signals associated with segment 402.Therefore, during a read or program operation for segment 400, only oneof bitlines BL1 _(—) e and BL1 _(—) o will be coupled to page buffer212. It is noted that selection signals A_SELe and A_SELo are sharedwith the other bitline selection circuits in segment 402.

The program disable circuit 407 includes high voltage n-channelshielding transistors 408 and 410 serially connected between bitlinesBL1 _(—) e and BL1 _(—) o. The common terminal of transistors 408 and410 is connected to a program inhibit voltage level PWRBL, which isselectively coupled to either BL1 _(—) e and BL1 _(—) o during either aread or a program operation by activating shielding signals A_SHLDe orA_SHLDo respectively. For example, when BL1 _(—) e is selected for aprogramming operation, then BL1 _(—) o will be biased to VCC, or anyother voltage sufficient to inhibit programming, through PWRBL toinhibit programming to any memory cells coupled to BL1 _(—) o. Duringread operations on the other hand, PWRBL will be set to VSS to bias theunselected bitlines to VSS. The corresponding program disable circuitand even/odd bitline selection circuit for BL1_e and BL1_o isidentically configured to the previously described circuits, except thatthey are controlled by a different set of signals, namely B_SHLDe,B_SHLDo, B_SELe and B_SELo. PWRBL can be driven by an inverter circuitsupplied by VCC and VSS, or the program inhibit voltage and VSS, andcontrolled by a programming related signal. As will be shown in FIG. 8,a row address is used to generate the selection signals and theshielding signals for either segments 400 or 402, while a column addressis used to generate the even and odd selection and shielding signals.

FIG. 8 is an example decoding circuit which can be used for generatingthe selection signals and the shielding signals for the bitlineselection circuit 405 and the program disable circuit 407 in bothsegments 400 and 402 shown in FIG. 7B. Those skilled in the art willunderstand that the example embodiment of FIG. 8 is one decodingconfiguration, and that other decoding configurations can be used forachieving the same result.

Referring to FIG. 8, decoding circuit 500 includes four identicallyconfigured sub-decoders 502, 504, 506 and 508. The description of eachsub-decoder will be made with reference to the logic circuits ofsub-decoder 502, since all the sub-decoders are identically configured.Each sub-decoder, such as sub-decoder 502, includes an address decodingNAND gate 510, a shield enable NAND gate 512, inverters 514 and 516, andlocal charge pumps 515 and 517. Address decoding NAND gate 510 receivesa row address R_ADDR and a column address C_ADDR, and provides an outputthat is provided to one input terminal of shield enable NAND gate 512and to inverter 516. The output of inverter 516 is boosted by localcharge pump 517 to provide the even signal A_SELe, which is received byall the bitline selection circuits in segment 400. Therefore, A_SELe isan address decoded signal driven to the active logic level in responseto a particular combination of R_ADDR and C_ADDR. In the presentexample, this occurs when both R_ADDR and C_ADDR are at the high logiclevel. The second input terminal of shield enable NAND gate 512 receivesa program status signal PGM, which is decoded with the output of addressdecoding NAND gate 510. The output of NAND gate 512 is driven byinverter 514 and boosted by local charge pump 515 to provide signalA_SHLDe.

The purpose of the local charge pumps is to drive the high logic levelof the signals above the supply voltage VCC. As previously mentioned,during a read operation the unselected bitlines are biased to VSS viaPWRBL at VSS. For example, one of A_SHLDe or A_SHLDo will be driven toVCC, which is sufficient for discharging the unselected bitline to VSS.However during a program operation where unselected bitlines are to bebiased to VCC through PWRBL, signals A_SHLDe or A_SHLDo at VCC will beinsufficient for passing the full VCC level to the bitlines. Therefore,the local charge pumps will ensure that the gate terminals of theshielding transistors, such as shielding transistors 408 and 410, can bedriven above VCC. This same principle applies to the bitline selectiontransistors, such as transistors 404 and 406. During the programmingoperation, the page buffer will drive the common bitlines to either VCCor VSS, depending on the data to be programmed. In order to fully passVCC to the selected bitlines, signals A_SELe and A_SELo are driven to avoltage level above VCC.

By example, signal A_SHLDe is a signal that is driven to the activelogic level when the particular combination of R_ADDR and C_ADDR ispresent, i.e., both are at the high logic level. While C_ADDR is asingle bit signal in the present embodiment for coupling one of twobitlines to the common bitline (CBL_S1_1 for example), those skilled inthe art will understand that the decoding circuit of FIG. 8 can beconfigured to receive C_ADDR of any number of bits. Hence, one of manybitlines can be selectively coupled to the common bitline, provided theprogram disable circuits and the bitline selection circuits are expandedto include more n-channel transistors corresponding to transistors 404,406, 408 and 410.

Sub-decoder 504 is identically configured to sub-decoder 502, exceptthat its address decoding NAND gate 510 receives the opposite logiclevel of C_ADDR via inverter 518 for driving A_SELo to the active logiclevel and A_SHLDo to the active logic level when PGM is at the activelogic level. Sub-decoders 502 and 504 drive signals for segment 400since the same row address R_ADDR is used. Therefore sub-decoders 504and 506 will drive signals B_SELe, B_SHLDe; and B_SELo, B_SHLDo forsegment 402 since they receive the opposite state of R_ADDR via inverter520. Because sub-decoder 506 receives C_ADDR and sub-decoder 508receives the opposite state of C_ADDR via inverter 518, the even and oddselection and shield signals are provided.

Program status signal PGM is shared by all the shield enable NAND gates512 of the sub-decoders 502, 504, 506 and 508, to globally enable ordisable production of its respective shielding signals. In the presentembodiment, PGM is at the active high logic level during a programoperation to ensure that the proper shielding signal is activated sothat the non-selected bitline adjacent to the selected bitline, iscoupled to PWRBL to inhibit programming of memory cells connected to it.In an alternate method of operation, PWRBL can be inhibited from beingapplied to all the bitlines during a read operation, because thenon-selected bitline can be subsequently selected by changing the columnaddress C_ADDR while the selected wordline remains active, to read moredata from the memory array.

With this understanding of the decoding scheme shown in the embodimentsof FIG. 7 and FIG. 8, a read operation and a write operation of thecircuits shown in FIG. 7 can be easily understood. In a read operation,PGM is at the low logic level and a wordline is activated in all thesegments, including segments 400 and 402, of sector 202 or 206 of FIG.5. A current corresponding to a stored data state in the correspondingmemory cells is then provided to a respective bitline. If the rowaddress activates a wordline in segment 400, then the selection signalsB_SELe, B_SELo, B_SHLDe and B_SHLDo for segment 402 are disabled. Inresponse to a specific column address C_ADDR, one of the even or oddbitlines of each set of bitlines is coupled to a corresponding commonbitline. The page buffer 212 will sense and latch the data of all thecommon bitlines of the sector, but will provide only the data from onesegment in parallel on data lines L_DL[1:n]. The common datalinesL_DL[1:n] are shared by all the segments in sectors 200 and 206, and aswill be described later, the data from exactly one segment is coupled todatalines L_DL[1:n]. More specifically, all the data of either segment400 or 402 is output by sequentially enabling the page buffer 212segments to couple data to datelines L_DL[1:n].

A program operation is the reverse process, except now PGM is at thehigh logic level. Write data will be provided on data lines L_DL[1:n] tobe latched by page buffer 212 and driven onto the respective commonbitlines. If a wordline in segment 400 is selected for programming, thenthe selection signals A_SELe, A_SELo, A_SHLDe and A_SHLDo are disabled.It is noted that since no wordline in segment 402 is selected, there isno need to apply the PWRBL program inhibit voltage to the bitlines,thereby reducing power consumption. A column address C_ADDR is providedand the common bitlines will be coupled to the selected bitlines of theeven or odd bitlines, while the PWRBL voltage is applied to thenon-selected bitlines.

FIG. 9 is a circuit schematic illustrating an example local charge pumpused in the sub-decoders of FIG. 8. Local charge pump 550 includes adepletion mode n-channel pass transistor 552, a native n-channeldiode-connected boost transistor 554, a high breakdown voltage n-channeldecoupling transistor 556, a high breakdown voltage n-channel clamptransistor 558, a NAND logic gate 560, and a capacitor 562. NAND logicgate 560 has one input terminal for receiving input terminal IN andanother input terminal for receiving controlled signal φp, for drivingone terminal of capacitor 562. Pass transistor 552 is controlled by thecomplement of signal PGM of FIG. 8, referred to as PGMb. The commonterminals of decoupling transistor 556 and clamp transistor 558 arecoupled to high voltage VH.

The operation of local charge pump 550 is now described. During a readoperation, PGMb is at the high logic level and φp is maintained at thelow logic level. Therefore, circuit elements 562, 554, 556 and 558 areinactive, and the output terminal OUT reflects the logic level appearingon the input terminal IN. During a program operation, PGMb is at the lowlogic level, and φp is allowed to oscillate between the high and lowlogic levels at a predetermined frequency. If the input terminal IN isat the high logic level, then capacitor 562 will repeatedly accumulatecharge on its other terminal and discharge the accumulated chargethrough boost transistor 554. Decoupling transistor 556 isolates VH fromthe boosted voltage on the gate of boost transistor 554. Clamptransistor 558 maintains the voltage level of output terminal OUT atabout VH+Vtn, where Vtn is the threshold voltage of clamp transistor558. The local charge pump 550 shown in FIG. 9 is one example circuitwhich can be used to drive signals to a voltage levels higher than thesupply voltage VCC, but persons skilled in the art will understand othercharge pump circuits can be used with equal effectiveness. Table 2 belowshows example bias conditions for the local charge pump 550 during readand program operations.

TABLE 2 Read Program Selected Unselected Selected Unselected IN Vcc VssVcc Vss PGMb Vcc Vcc Vss Vss φP Vss Vss Oscillation Oscillation VH VccVcc ~5 V ~5 V OUT Vcc Vss 5 V + Vtn Vss

As previously mentioned, minimized circuit area consumption of the pitchlimited circuits will result in a reduced area of the memory bank. Inthe present embodiments, this is achieved by sharing one page bufferwith both adjacent sectors 202 and 206, and by minimizing the amount ofcolumn select circuitry used for coupling the page buffer 212 to thedatalines L_DL[1:n]. While the previously proposed column decodingscheme shown in FIG. 3 can be used to couple the data from the pagebuffer 212 of FIG. 5 or 7A to the datalines L_DL[1:n], the plurality offirst and second stage pass transistors will require valuable circuitarea. To further minimize circuit area, a self-decoding column selectcircuit is used for coupling data from each page segment of sectors 202and 206 to the datalines L_DL[1:n].

FIG. 10 is a block diagram showing a functional implementation of aself-decoding column select circuit integrated into a page buffercircuit, according to an embodiment of the present invention.Self-decoding page buffer 600 can be used in place of both page buffers212 and 214 in FIG. 5 and page buffer 212 in FIG. 7. Self-decoding pagebuffer 600 will sequentially couple data from each segment stored inpage buffer 212 to the datalines L_DL[1:n], in response to a singlecolumn select bit COL_BIT that is shifted through the self-decoding pagebuffer 600. The self-decoding page buffer 600 includes several pagebuffer stages 614, 616 and 618, of which only three are shown in FIG.10. As shown in FIG. 10, the page buffer stages 614, 616 and 618 includesequential enablers 602, 604 and 606, and segment page buffers 608, 610and 612. Accordingly, each sequential enabler is paired with one segmentpage buffer for controlling the segment page buffer. For example,sequential enabler 602 is paired with segment page buffer 608. In theembodiment of FIG. 10, it is assumed that there are up to m pagesegments (400 and 402) in sectors 202 and 206 of FIG. 7A, and thereforethere are m corresponding self-decoding page buffer stages, of whichonly the first, second and last self-decoding page buffer stages ofself-decoding page buffer 600 are shown. The variable m can be anyinteger value greater than 0, and is selected based on the memory arrayarchitecture.

Each self-decoding page buffer stage is responsible for coupling itscommon bitlines to datelines L_DL[1:n]. Accordingly, segment page buffer608 couples common bitlines CBL_S1 _(—)[1:n] of the first segment toL_DL[1:n], segment page buffer 610 couples common bitlines CBL_S2_(—)[1:n] of the second segment to L_DL[1:n], and segment page buffer612 couples common bitlines CBL_Sm_(—)[0:n] of the mth (last) segment toL_DL[1:n]. Each segment page buffer is controlled by its respectivesequential enabler, and each sequential enabler will be enabled tocouple its common bitlines to L_DL[1:n] when the single column selectbit COL_BIT is received.

In the present embodiment, each sequential enabler receives controlsignals such as complementary reset signals RST and RSTb, decode enablesignal YENb, and complementary clock signals φ and φb. In their activestates, signals RST, RSTb and YENb enable the sequential enabler. In thefirst self-decoding page buffer stage 614, the input terminal INreceives COL_BIT, which will be provided through output terminal OUT inresponse to clock signals φ and φb. Because each sequential enabler isconnected in series to a preceding sequential enabler by connecting itsinput terminal IN to the output terminal OUT of the preceding sequentialenabler, column select bit COL_BIT is eventually shifted from the firstsequential enabler 602 to the last sequential enabler 606. Therefore,each segment page buffer will couple its common bitlines to L_DL[1:n] insequence, in response to COL_BIT. In the present embodiment, COL_BIT isa high logic level bit, but can be a low logic level bit as well.

FIG. 11 is a block diagram showing the details of one self-decoding pagebuffer stage, such as self-decoding page buffer stage 614 for example.The remaining self-decoding page buffers stages are identicallyconfigured. Self-decoding page buffer stage 614 includes sequentialenabler 602 shown in FIG. 10, and page buffer units 650, 652, 654 and660. In the present example, page buffer unit 660 is the last pagebuffer unit in page buffer stage 614. Sequential enabler 602 is asimplified block diagram that omits the control signals in order tosimplify the diagram. There are a total of n page buffer units, whereeach couples one common bitline to one dataline. For example, pagebuffer unit 650 couples CBL_S1_1 to L_DL1. All page buffer units areenabled to electrically couple their common bitline to a respectivedataline in response to an active column enable signal Y-SEL. Y-SEL isdriven to the active logic level by sequential enabler 602 in responseto COL_BIT, which will be subsequently passed on to the next sequentialenabler in response to the clock signals φ and φb (not shown).

FIG. 12 is a circuit schematic of the sequential enabler 602 of FIGS. 10and 11. In the present embodiment all sequential enablers are identicalin configuration. Each sequential enabler is implemented as amaster/slave flip-flop 700. Master/slave flip-flop 700 includes a firsttransmission gate 702, a pair of cross-coupled inverters 704 and 706, asecond transmission gate 708, a second pair of cross-coupled inverters710 and 712, first and second reset devices 714 and 716, and a NOR logicgate 718. Master/slave flip-flop 700 is enabled when control signalsRST, RSTb and YENb are at the high, low and low logic levels,respectively. When disabled, OUT and Y-sel will be at the low logiclevel as reset devices 714 and 716 will be turned on and at least oneinput to NOR logic gate 718 will be at the high logic level. Thesecontrol signals can be controlled by the command decoder or othersimilar logic, and synchronized to ensure that read data is properlyapplied to the datalines and program data is properly applied to thecommon bitlines.

First transmission gate 702 passes a received signal, such as COL_BIT,on input terminal IN when clock signals φ and φb are at the high and lowlogic levels respectively. Cross coupled inverters 704 and 706 willlatch the signal and pass it to the second pair of cross-coupledinverters 710 and 712 via second transmission gate 708 when φ and φbhave switched to the low and high logic levels respectively. Theinverted state of the input signal (COL_BIT) is received by NOR logicgate 718, which is then inverted again by enabled NOR logic gate 718 todrive Y-sel to the high logic level. Output terminal OUT will passCOL_BIT to the next master/slave flip-flop at substantially the sametime that Y-sel is driven to the active high logic level. It is noted,however, that the next master/slave flip-flop will latch COL_BIT whenclock signal φ is at the high logic level.

FIG. 13 is a circuit schematic of a page buffer unit, such as pagebuffer unit 650 shown in FIG. 11. Referring to FIGS. 11 to 13, all pagebuffer units are identically configured. Page buffer unit 750 includes aprecharge circuit, a sense circuit and a dataline coupling circuit. Theprecharge circuit includes a precharge device 752 for precharging thecommon bitline CBL_S[1:m]_(—)[1:n] to VDD in response to prechargesignal PREb. The sense circuit includes a latch reset device 754, alatch sense enable device 756, and a latch enable device 758 connectedin series between VDD and VSS, and cross-coupled inverters 760 and 762.Latch reset device 754 is controlled by latch reset signal RSTPB forresetting the latched state of cross-coupled inverters 760 and 762.Latch enable device 758 is controlled by latch enable signal LCHD forenabling sensing of the current on the common bitlineCBL_S[1:m]_(—)[1:n]. Cross-coupled inverters 760 and 762 have a firstcommon node “a” connected to the shared terminals of latch reset device754 and latch sense enable device 756, and a second common node “b”coupled to the dataline coupling circuit. The dataline coupling circuitincludes a bitline isolation device 764 and a column select device 766connected in series between common bitline CBL_S[1:m]_(—)[1:n] anddataline L_DL[1:n]having common node “b” at the shared terminals ofdevices 764 and 766. Bitline isolation device 764 is controlled bysignal ISOPB while column select device 766 is controlled by columnselect signal Y-sel. Signals PREb, RSTPB, ISOPB and LCHD can begenerated from the control block 106 of FIG. 4A.

The operation of page buffer unit 650 during a read operation is nowdescribed. While latch enable signal LCHD is at the inactive low logiclevel, signal RSTPB is driven to the low logic level to resetcross-coupled inverters 760 and 762 such that node “b” is set to the lowlogic level. Accordingly, node “a” is at the high logic level duringthis reset state. The common bitline CBL_S[1:m]_(—)[1:n] is prechargedto VDD by driving PREb to the low logic level, thereby turning onprecharge device 752. After a wordline is activated and the selectedbitline is coupled to CBL_S[1:m]_(—)[1:n], ISOPB is driven to the highlogic level and signal LCHD will be driven to the high logic level toenable sensing of the voltage on CBL_S[1:m]_(—)[1:n]. If the selectedmemory cell is unprogrammed, then the VDD precharge level ofCBL_S[1:m]_(—)[1:n] will flip node “b”. On the other hand, if theselected memory cells is programmed, then the VDD precharge level ofCBL_S[1:m]_(—)[1:n] will discharge towards VSS. When the sensing periodis ended, LCHD returns to the low logic level, and Y-sel is eventuallydriven to the high logic level to couple the latched data to L_DL[1:n].

The operation of page buffer unit 650 during a program operation is nowdescribed. In a program operation, latch enable signal LCHD is not usedand remains at the inactive low logic level, while signal RSTPB isdriven to the low logic level to reset cross-coupled inverters 760 and762 such that node “b” is set to the low logic level. The common bitlineCBL_S[1:m]_(—)[1:n] is precharged to VDD by driving PREb to the lowlogic level, thereby turning on precharge device 752. Program data isdriven onto L_DL[1:n], and is latched by cross-coupled inverters 760 and762 when Y-sel is driven to the high logic level. Signal ISOPB is drivento the high logic level to couple node “b” to CBL_S[1:m]_(—)[1:n]. Theprogrammed state of the memory cells coupled to the selected wordlinewill then depend on the logic level of node “b”.

A unique feature of page buffer unit 750 is the single column selectdevice 766 that directly couples the cross-coupled inverters 760 and 762to L_DL[1:n]. The single column select device is simpler and occupies asmaller circuit area than the column select devices 72 and 74 of FIG. 3.Accordingly, a single corresponding Y-sel signal, generated by acorresponding sequential enabler such as sequential enabler 602, is allthat is needed for coupling L_DL[1:n] to node “b”. The previousdescription of the operation of the page buffer unit 650 during read andprogram operations are example operations, and those skilled in the artwill understand that the same circuit can be operated with variations insignal activation sequences. The page buffer unit 650 can be implementedwith alternate circuit configurations that perform sensing and latchingfunctionality for read data, and latching functionality for programdata.

Following is a discussion of the operation of self-decoding page buffer600 of FIG. 10, which uses the circuit embodiments shown in FIGS. 11 to13. Reference is made to the sequence diagram shown in FIG. 14, whichshows signal traces for control signals used by the sequential enabler,and signal traces of the column select bit COL_BIT as it is passed, orshifted, from one sequential enabler to a subsequent sequential enabler.The shown control signal traces include common complementary clocksignals φ and φb, common complementary reset signals RST and RSTb, andcommon decode enable signal YENb. The signal traces for the inputterminal “In”, the output terminal “Out” and the Y-sel output of a firstsequential enabler are shown, as are the signal traces for the outputterminal “Out” and the Y-sel output for subsequent sequential enablers.In FIG. 14, the signals associated with the first, second and thirdsequential enablers are appended with the numbers 1, 2 and 3respectively, while the last (mth) sequential enabler has its associatedsignals appended with the letter m.

Starting at time t₀, reset signal RST is pulsed to the high logic levelwhile complementary signal RSTb is pulsed to the low logic level toreset all the sequential enablers. In the present embodiment, RST andRSTb are pulsed on a rising edge of clock signal φ. As shown in theexample sequential enabler circuit implementation of FIG. 12, the latchconsisting of inverters 704 and 706 has its input side coupled to VSSwhile the latch consisting of inverters 710 and 712 has its input sidecoupled to VDD, in response to the complementary reset signal pulses.Although the reset signal pulses are short in duration, transmissiongate 708 is open while clock signal φ is at the high logic level.Therefore the two latch circuits drive each other to the reset states.Decode enable signal YENb remains at the inactive high logic level tomaintain Y-sel at the low logic level.

Following at time t₁, the input terminal In_1 of the first sequentialenabler 1 is pulsed to the high logic level, which corresponds to theapplication of column select bit COL_BIT. COL_BIT is latched byinverters 704 and 706 when φ is at the high logic level. At time t₂, φtransitions to the low logic level to shift COL_BIT to inverters 710 and712 to drive output terminal “Out” to the high logic level. At time t₃,clock signal φ transitions to the low logic level and COL_BIT appearingon Out_1 will be latched by the sequential enabler 2, since its In_2input terminal is connected to Out_0. The signal trace for In_2 and thesubsequent sequential enablers are not shown in order to simplify thesequence diagram. It is noted that at time t₃, input terminal “In_1” isheld at the low logic level since each sequential enabler will receiveCOL_BIT only once per decode cycle, where one decode cycle ends afterthe last common bitline is coupled to the dataline. In the example ofFIG. 10 this can be CBL_Sm_n. This means that for subsequent transitionsof clock signal φ, a low logic signal will be latched by both latchcircuits of the sequential enabler. In other words, an inactive lowlogic level COL_BIT is received by the sequential enabler 2.

Returning to the first sequential enabler 1, YENb is pulsed to the lowlogic level at time t₄ to enable NOR logic gate 718, which then drivesY-Sel_1 to the high logic level for the same approximate duration thatYENb is at the low logic level. When Y-Sel_1 is at the high logic level,column select device 766 of page buffer unit 750 will be turned on tocouple its corresponding common bitline to a dateline. At time t₅, clocksignal φ transitions to the low logic level, causing output terminalOut_2 of sequential enabler 2 to be driven to the high logic level. Aspreviously remarked, sequential enabler 2 had received COL_BIT at timet₃. At substantially the same time, output terminal Out_1 of sequentialenabler 1 falls to the low logic level as it had latched the inactiveCOL_BIT signal. Subsequently, Y-Sel_2 will be pulsed to the high logiclevel in response to low logic level pulse of YENb. This process repeatsuntil the last sequential enabler pulses Y-Sel_m to the high logiclevel.

In the embodiment shown in FIG. 5, Y-Sel_m is the last column selectsignal of page buffer 212 to be enabled. If the same logical wordline isdriven in Sector 208, then the output terminal Out_m can be coupled tothe first sequential enabler in page buffer 214, where the sequentialactivation of column select signals would continue. Those skilled in theart will understand that parallel/serial data conversion selector 216 iscontrolled to serialize the data from R_DL[1:n] instead of L_DL[1:n].Therefore, by activating the column enable signals (Y-Sel_(—)[1:m]) insequence, all the bits of data associated with a selected wordline caneither be read from it or programmed to it. More specifically, as eachY-Sel signal is activated, sets of nbits of data are iterativelyprovided onto datelines L_DL[1:n], and then subsequently serialized byparallel/serial data conversion selector 216 as GLOB_DATA. Those skilledin the art will understand that counter 306 of FIG. 6 should completethe serialization of the datelines L_DL[1:n] (or R_DL[1:n]) within oneperiod of clock signal φ, hence the selection of the frequenciesgoverning the operation of these circuits will be selected to ensureproper operation of the circuits.

While the example embodiments of the page buffer shown in FIGS. 7A to 13shows their implementations in the serial data path core architecture,it is noted that they can be used in illustrated Flash memoryarchitectures that do not employ a serial data path core architecture.For example, the standard Flash memory array can be designed to bedivided into top and bottom halves, analogous to the sectors shown inthe figures, and the page buffer of the presented embodiments positionedin between. Column selection devices and decoding circuitry formultiplexing the top bitlines and bottom bitlines to common bitlines canbe implemented in the manner shown and described in the presentembodiments. While each self-decoding page buffer cell of the 2D pagebuffer shown in FIGS. 10 and 11 include a sequential enabler forproviding a Y-sel signal for the page buffer unit, any address decodedsignal can be used instead. The specific decoding configuration willdepend on the selected data output architecture being implemented. Forexample, a grouping of successive page buffer units can receive the sameaddress decoded Y-sel signal, or each page buffer unit of a groupingreceives a different address decoded Y-sel signal.

The previous discussion illustrates direct bank to serial data pathoperation, such as memory bank 104 and serial data path 102 of FIG. 4A.According to another embodiment of the present invention, the serialcore memory system 100 includes two memory banks both accessible by theserial data path 102. With reference to FIG. 5 for example, the singlememory bank 200 would be replaced by two identically configured memorybanks. Naturally, two memory banks will increase the density of thememory device, and according to another embodiment of the presentinvention, both memory banks can be coupled to each other to realizedirect bank-to-bank data transfers. Bank-to-bank transfers are ideallysuited for advanced operations such as wear leveling control, where datacan be copied to the other memory bank if the finite program/erasecycles for a portion of the current memory bank is about to be reached.Otherwise, in the worst case scenario, the data would have to be readout from one bank through the serial data path 102 and back to thememory controller, which then sends the data back to the other bank ofthe same memory device. Those skilled in the art will understand thatthis sequence of operations will impact performance of the memorysystem. Wear leveling control is just an example of one operation thatcan take advantage direct memory bank transfers, but any operation wheredata is moved or copied from one bank to another will benefit from adirect bank to bank transfer architecture.

FIG. 15 is a block diagram showing a direct bank to bank transferarchitecture according to an embodiment of the invention. The presentembodiment includes two identically configured memory banks 800 and 802,and a serial transfer switch 804. In the example of FIG. 15, memorybanks 800 and 802 are identical in configuration as memory bank 200 ofFIG. 5, and as such, includes the same features that have beenpreviously described. Memory bank 800 provides and receives serial datavia a serial data signal called BANK1_DATA while memory bank 802provides and receives serial data via a serial data signal calledBANK2_DATA. BANK1_DATA and BANK2_DATA are coupled to serial transferswitch 804, which selectively couples one of the two to GLOB_DATAdepending on which memory bank is being accessed for a read or a programoperation. GLOB_DATA is analogous to the same named signal in FIG. 5,which is coupled to a serial data path, such as serial data path 102 ofFIG. 5. While signal GLOB_DATA is considered a serial global data signalthat is coupled to the serial data path of a memory device, such asserial data path 102 of FIG. 4A, serial data signals BANK1_DATA andBANK2_DATA are considered local serial data signals.

The operation of serial transfer switch 804 described above is called anormal mode of operation. In a direct transfer mode of operation,BANK1_DATA and BANK2_DATA are directly coupled to each other.Accordingly, in the direct transfer mode of operation, the page buffersof memory bank 800 and 802 will be synchronized such that data providedfrom the page buffers of one memory bank are latched in the page buffersof the other memory bank. For example, the same clock signals used bythe sequential enabler 700 of FIG. 12 can be shared between memory banks800 and 802, and the CLK signal used in parallel/serial data conversionselector 216 of FIG. 6 can be shared between memory banks 800 and 802.

FIG. 16 is a circuit schematic of serial transfer switch 804 of FIG. 15,according to one embodiment. Serial transfer switch 804 includes a databank selector 810, and transmission gates 812, 814 and 816. Transmissiongate 812 couples BANK1_DATA to a first terminal of data bank selector810, while transmission gate 814 couples BANK2_DATA to a second terminalof data bank selector 810. Both transmission gates 812 and 814 areturned on when complementary signals DIR and DIRb are at the inactivelow and high logic levels respectively. Transmission gate 816 couplesBANK1_DATA and BANK2_DATA directly to each other when DIR and DIRb areat the active high and low logic levels respectively. Data bank selector810 is controlled by selection signal BANK_SEL, to couple eitherBANK1_DATA or BANK2_DATA to GLOB_DATA. The circuit of serial transferswitch 804 is an example of one circuit implementation, and other knowncircuits can be used to achieve the same functionality. For example,data bank selector 810 can be implemented with amultiplexor/demultiplexor circuit that is well known in the art. SignalsDIR and DIRb can be generated by the control block 106 of the memorydevice of FIG. 4A in response to a specific command.

The direct bank to bank transfer architecture is scalable to includemore than two memory banks. For example, pairs of memory banks asconfigured in FIG. 15 can be linked together with another serialtransfer switch positioned between the two pairs to couple the finalGLOB_DATA signal to the serial data path. Accordingly, the memory bankconfiguration shown in FIG. 15 can replace the single memory bank 104 ofFIG. 4A.

The serial core memory system 100 of FIG. 4A is an example of a memorydevice having a single serial data path for interfacing with othermemory devices. U.S. Patent Publication No. 20070076479 describes a highperformance memory system which can execute substantially concurrentoperations as it includes a two separate serial interface circuits. Thisprinciple can be applied to the serial core memory system 100 of FIG. 4Ato realize a high density and high performance memory system with adirect bank to bank transfer architecture.

FIG. 17 is a block diagram of a multi-bank serial core memory systemhaving two independent serial data paths. Memory system 900 includes afirst serial data path 902, a second serial data path 904, controlblocks 906 and 908, and memory banks 910, 912, 914 and 916. Locatedbetween memory banks 910 and 912 is a first serial transfer switch 918.Located between memory banks 914 and 916 is a second serial transferswitch 920. The first and second serial data paths 902 and 904correspond to the serial data path 10 shown in FIG. 4A, while thecontrol blocks 906 and 908 correspond to the control block 106 shown inFIG. 4A. The high voltage generator shown in FIG. 4A is omitted tosimplify the schematic, however those skilled in the art will understandthat a high voltage generator and other circuits will be required toenable proper functionality of the system. The first serial data path902 receives DATA/CMD_IN_1 and provides DATA/CMD_OUT_1 while secondserial data path 904 receives DATA/CMD_IN_2 and provides DATA/CMD_OUT_2.Each of the first and second serial data paths 902 and 904 includes aserial I/O interface 922, a data arbitrator 924, and a data switcher926. All these circuits have been previously described, as have theirfunctions.

Generally, circuit blocks 902, 906, 910, 912 and 918 operate as a singleunit, while circuit blocks 904, 908, 914, 916 and 920 operate as anothersingle unit. This means that operations can be executed in either unitindependently of the other, and concurrently with each other. Thepresence of data switchers 926 in both serial data paths 902 and 904 nowpermits the serial data paths to access every memory bank. As shown inFIG. 17, there is a single bit direct transfer line 928 coupled betweendata switchers 926. Therefore, memory banks 910 and 912 can be coupledto serial data path 904 while memory banks 914 and 916 can be coupled toserial data path 902. Furthermore, data from memory banks 910 and 912can be directly transferred to memory banks 914 and 916, and vice versa,through the direct transfer line 928.

Direct memory transfer operations are advantageous, since the data doesnot need to be read out of the memory device before being reprogrammedto a different bank of the same memory device. For example, page copy orblock copy operations can be efficiently executed because as datacorresponding to one page is read from a source bank, the data is loadedinto the target bank at substantially the same time.

Therefore, there are several different circuits of the serial corememory system that will minimize circuit area consumption whileimproving performance relative to memory devices employing a traditionalparallel data path core. First is the self-decoding column selectcircuit for quickly transferring data from the bitlines to datalines.Second is the shared page buffer which is coupled to two sectors of amemory array. Third is the serial data path for coupling a serialbitstream of data between external input/output interface pins and atleast one memory bank 104 of FIG. 4A. Fourth are the serial transferswitches and data switches that couple memory banks to each other or todifferent serial data paths. Since data is transferred between theexternal input/output pins and the memory sectors in serial format, andonly converted to parallel format within the memory bank, significantcircuit area is conserved. This is because only single bi-directionalserial data lines, such as direct transfer line 928, bidirectionalserial data lines 110 and the serial data paths 902 and 904 are used fortransporting the data serially instead of with a plurality of paralleldata lines.

The previously described embodiments of the serial core memory systemcan be implemented in discrete memory devices, or can be embedded in asystem on chip (SOC) or system in package (SIP) device. In a discretememory device implementation, multiple memory devices having the abovedescribed serial core memory system embodiments can be used in theserial interconnection 5 of FIG. 1A. A single packaged deviceimplemented as an SOC can have multiple instances of the memory systemconnected serially in the same configuration shown in FIG. 1A. A singlepackaged device implemented as an SIP can have multiple chips connectedserially in the same configuration shown in FIG. 1A.

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe embodiments of the invention. However, it will be apparent to oneskilled in the art that these specific details are not required in orderto practice the invention. In other instances, well-known electricalstructures and circuits are shown in block diagram form in order not toobscure the invention. For example, specific details are not provided asto whether the embodiments of the invention described herein areimplemented as a software routine, hardware circuit, firmware, or acombination thereof.

In the above-described embodiments, the operation has been describedbased on the active “high” signals for the purpose of simplicity. Theymay be designed to perform the operation based on the “low” activesignals, in accordance with a design preference.

In the embodiments described above, the device elements and circuits arecoupled or connected to each other as shown in the figures, for the sakeof simplicity. In practical applications of the present invention toapparatus, devices, elements, circuits, etc. may be coupled or connecteddirectly to each other. As well, devices, elements, circuits etc. may becoupled or connected indirectly to each other through other devices,elements, circuits, interfaces, etc., necessary for operation of theapparatus. Thus, in actual configuration, the circuit elements anddevices are directly or indirectly coupled with or connected to eachother.

The above-described embodiments of the invention are intended to beexamples only. Alterations, modifications and variations can be effectedto the particular embodiments by those of skill in the art withoutdeparting from the scope of the invention, which is defined solely bythe claims appended hereto.

1. A memory bank comprising: a first memory sector having memory cellsconnected to first bitlines and first wordlines, the first bitlinesbeing arranged as m segments where m is an integer value greater than 0;a second memory sector having memory cells connected to second bitlinesand second wordlines, the second bitlines being arranged as m segments;a page buffer disposed between the first memory sector and the secondmemory sector for selectively coupling one of the first bitlines and thesecond bitlines of each of the m segments to a predetermined number ofdatelines.
 2. The memory bank of claim 1, wherein a read operation isexecuted by activating a wordline of one of the first wordlines in thefirst memory sector and the second wordlines in the second memory sectorin response to a row address, at least two memory cells being coupled tothe first bitlines when the wordline is one of the first wordlines, andat least two memory cells being coupled to the second bitlines when thewordline is one of the second wordlines, selectively coupling onebitline of the first bitlines and the second bitlines to a commonbitline in response to a column address, sensing the common bitline withthe page buffer, and providing data corresponding to the sensed commonbitline onto one of the predetermined number of datelines.
 3. A pagebuffer for a memory bank comprising: a first self-decoding page bufferstage for sensing data from a first bitline, and for providing senseddata corresponding to the first bitline on a corresponding data line inresponse to an active column select bit latched in a clock signal state,the first self-decoding page buffer stage including an output terminalfor providing the active column select bit; and, a second self-decodingpage buffer stage having an input terminal for receiving the activecolumn select bit from the output terminal of the first self-decodingpage buffer stage, for sensing data from a second bitline, and providingsensed data corresponding to the second bitline on the correspondingdata line in response to the active column select bit latched in asubsequent clock signal state.
 4. The page buffer of claim 3, wherein aself-decoding operation is executed by latching the active column selectbit in the first self-decoding page buffer stage in response to anopposite clock signal state, providing the sensed data from the firstself-decoding page buffer stage and passing the active column select bitin response to the clock signal state, latching the active column selectbit in the second self-decoding page buffer stage in response to asubsequent opposite clock signal state, and providing the sensed datafrom the second self-decoding page buffer stage in response to thesubsequent clock signal state.
 5. The page buffer of claim 3, whereinthe first self-decoding page buffer stage includes a first segment pagebuffer for sensing data from the first bitline and providing the senseddata corresponding to the first bitline on the corresponding data linein response to a first enabling signal, and a first sequential enablerreceiving and latching the active column select bit and including theoutput terminal, the first sequential enabler providing in response tothe active column select bit being latched in the clock signal state thefirst enabling signal and the active column select bit from the outputterminal.
 6. The page buffer of claim 5, wherein the secondself-decoding page buffer stage includes a second segment page bufferfor sensing data from the second bitline and providing the sensed datacorresponding to the second bitline on the corresponding data line inresponse to a second enabling signal, and a second sequential enablerincluding the input terminal for receiving and latching the activecolumn select bit provided by the first sequential enabler, the secondsequential enabler providing in response to the active column select bitbeing latched in the subsequent clock signal state the second enablingsignal.
 7. The page buffer of claim 6, wherein first sequential enablerincludes bi-stable circuitry clocked by a clock signal having the clocksignal state and a complement of the clock signal state, the bi-stablecircuitry including an input for receiving and latching the activecolumn select bit during the complement of the clock signal state, theoutput terminal for providing the active column select during the clocksignal state, and a column select output for providing the firstenabling signal having a logic state corresponding to the active columnselect bit during the clock signal state.
 8. The page buffer of claim 6,wherein the first segment page buffer includes a page buffer unit,connected to the first bitline and the corresponding data line.
 9. Thepage buffer of claim 8, wherein the page buffer unit includes sensecircuitry for sensing data of the first bitline, and a data linecoupling circuit for coupling sensed data from the sense circuitry tothe corresponding data line in response to the first enabling signal.10. The page buffer of claim 9, wherein the sense circuitry includes aprecharge circuit for precharging the first bitline.
 11. The page bufferof claim 9, wherein the sense circuitry includes a sensor for sensingthe data of the first bitline.
 12. The page buffer of claim 11, whereinthe data line coupling circuit includes a column coupling device forcoupling the sensor to the corresponding data line in response to thefirst enabling signal.
 13. The page buffer of claim 11, wherein the dataline coupling circuit includes an isolation device for isolating thesensor from the first bitline when the first bitline is beingprecharged.
 14. The page buffer of claim 6, wherein the second segmentpage buffer includes a page buffer unit, connected to the second bitlineand the corresponding data line.
 15. The page buffer of claim 14,wherein the page buffer unit includes sense circuitry for sensing dataof the second bitline, and a data line coupling circuit for providingsensed data from the sense circuitry to the corresponding data line inresponse to the second enabling signal.
 16. The memory bank of claim 1,further including common bitlines coupled to the page buffer, each ofthe common bitlines coupled to at least one segment of the firstbitlines and to at least one segment of the second bitlines.
 17. Thememory bank of claim 16, wherein the first bitlines includes a group offirst segments, and the second bitlines includes a group of secondsegments.
 18. The memory bank of claim 17, wherein the first memorysector includes a first bitline selection circuit for selectivelyconnecting one first segment of the group of first segments to a commonbitline of the common bitlines, and the second memory sector includes asecond bitline selection circuit for selectively connecting one secondsegment of the group of second segments to the common bitline of thecommon bitlines.
 19. The memory bank of claim 16, wherein the commonbitlines are grouped as a first set of common bitlines and a second setof common bitlines.
 20. The memory bank of claim 19, wherein the pagebuffer includes a first self-decoding page buffer stage for sensing datafrom the first set of common bitlines, and for providing sensed datacorresponding to each of the common bitlines of the first set of commonbitlines on the predetermined number of data lines in response to anactive column select bit latched in a clock signal state; and, a secondself-decoding page buffer stage for sensing data from the second set ofcommon bitlines, and for providing sensed data corresponding to each ofthe common bitlines of the second set of common bitlines on thepredetermined number of data lines in response to the active columnselect bit latched in a subsequent clock signal state.
 21. The memorybank of claim 20, wherein the first self-decoding page buffer stageincludes an output terminal for providing the active column select bitto an input terminal of the second self-decoding page buffer stage. 22.The memory bank of claim 21, wherein the first self-decoding page bufferstage includes a first segment page buffer for sensing data from thefirst set of common bitlines and providing the sensed data correspondingto each of the common bitlines of the first set of common bitlines onthe corresponding data lines in response to a first enabling signal, anda first sequential enabler receiving and latching the active columnselect bit and including the output terminal, the first sequentialenabler providing in response to the active column select bit beinglatched in the clock signal state the first enabling signal and theactive column select bit from the output terminal.
 23. The memory bankof claim 22, wherein the second self-decoding page buffer stage includesa second segment page buffer for sensing data from the second set ofcommon bitlines and providing the sensed data corresponding to each ofthe common bitlines of the second set of common bitlines on thecorresponding data lines in response to a second enabling signal, and asecond sequential enabler including the input terminal for receiving andlatching the active column select bit provided by the first sequentialenabler, the second sequential enabler providing in response to theactive column select bit being latched in the subsequent clock signalstate the second enabling signal.
 24. The page buffer of claim 8,wherein the first segment page buffer includes first page buffer unitseach connected to first bitlines and corresponding data line, and thesecond segment page buffer includes second page buffer units eachconnected to second bitlines and the corresponding data lines, the firstbitlines including the first bitline, the second bitlines including thesecond bitline, and the corresponding data lines including thecorresponding data line.
 25. The page buffer of claim 24, wherein allthe first page buffer units are enabled in response to the firstenabling signal and all the second page buffer units are enabled inresponse to the second enabling signal.